The present invention relates to a temperature control device for a refrigerating apparatus having both a heating means and a cooling means, and more particularly to a temperature control device for the refrigerating apparatus of the above-described type which is adapted for storage of cold storage goods as well as frozen goods.
FIG. 1 shows a prior art refrigerant circuit of a refrigerating apparatus having both a heating means and a cooling means to be used for a container, and one example of a temperature control system therefor. In the case of a cooling operation, a refrigerant gas at a high temperature and at a high pressure compressed by a compressor (1) which operates in response to an instruction from a temperature controller (10), discharges heat in a condenser (2), and after being condensed and liquified, the gas reaches a choke device (3). The refrigerant, after having its pressure reduced in this choke device, enters an evaporator (4), and while taking heat away from the air flowing through the evaporator (4), is evaporated into a gaseous state, and returns to the compressor to complete a refrigerating cycle.
During this cycle, the return air (6) of the refrigerating apparatus is cooled as it passes through the evaporator (4) and converted into a low-temperature air output (7) to be blown out into a storage area. Meanwhile, if the temperature of the return air (6) to the refrigerating apparatus, which is detected by a temperature detector (8), reaches a set temperature, then the temperature controller (10) stops the operation of the compressor (1) so as to interrupt the cooling operation. Subsequently, if the temperature within the storage area is raised as by invasion of heat or the like and hence the temperature of the return air (6) to the refrigerating apparatus becomes higher than another set temperature that is separate from the set temperature upon the stopping of the cooling operation, then the temperature controller (10) again instructs the compressor (1) to operate and so, the cooling operation is recommenced.
In the case of a heating operation, the refrigerating cycle is not actuated, but heating is effected by a heater (11). If a current is passed through the heater (11) in response to an instruction from the temperature controller (10), then the return air (6) to the refrigerating apparatus is heated by the heater (11) and converted into the air output (7) which is at a higher temperature an which is blown out into the storage area. If the temperature of the return air (6) to the refrigerating apparatus, which is detected by the temperature detector (8), reaches a predetermined temperature, then the temperature controller (10) stops the feeding of a current to the heater 11 so as to interrupt the heating operation. Meanwhile, if the temperature within the storage is lowered as by outflow of heat to the exterior and hence the temperature of the return air (6) to the refrigerating apparatus becomes lower than a set temperature by at least a predetermined value, then the temperature controller (10) again instructs the passing of a current through the heater (11), and so, the heating operation is recommenced.
This control method for the above-mentioned type of refrigerating apparatus having both a heating means and a cooling means has the following shortcoming. More particularly, in the case of the cooling operation, a difference between the temperature of the return air to the refrigerating apparatus and the temperature of the air output (7) into the storage area would be inevitably produced to the extent corresponding to a refrigerating capability. Since this refrigerating capability is set at such value that the lack of a refrigerating capability may not occur even in the case where the atmospheric air temperature is high, the return air (6) and the air output (7) always has a temperature difference to a certain extent (normally 2 or more degrees).
Therefore, in the event that goods which are intended to maintain a high quality by monitoring them so as to maintain a storage temperature that is very close to a freezing point such as, for instance, fruits, chilled beef, etc., the set temperature would be set higher than the freezing point by a value corresponding to the temperature difference so that the temperature of the air output (7) may not become lower than the freezing point of the goods. The cycles are repeated such that at the time point when the temperature of the return air (6) has reached this set temperature, the cooling operation is interrupted and at the time point when the return air temperature has risen by a predetermined value (normally, one or more degrees) with respect to the set temperature, the cooling operation is recommended.
Consequently, even when it is desirable to hold a temperature close to the freezing point, as is the case with long term preservation, a temperature difference is inevitably produced to a certain extent. Furthermore, in the case of the heating operation, since the temperature of the air output (7) becomes higher than that of the return air (6), the temperature difference (the difference between the freezing point and the holding temperature) would be further increased.
In order to compensate for this shortcoming, a system shown in FIG. 2 was proposed in the prior art. According to the system shown in FIG. 2, in the case where it is desired to preserve goods without causing their freezing and yet keep them at a temperature close to the freezing point of the goods, as is the case with cold storage goods, then temperature control is effected in response to a temperature detector (9) provided in the air output (7) blown into the storage area, whereas in the case of preserving goods which necessitate a sufficiently low temperature as is the case with frozen foods or the like, then temperature control is effected by employing the temperature detector (8) provided in the return air (6) to the refrigerating apparatus. It is to be noted that the temperature control by employing the temperature detector (8) is the same as that described in connection to the system shown in FIG. 1. The temperature control by making use of the temperature detector (9) is effected in the following manner.
In the case of the cooling operation, the refrigerating cycle when the temperature of the air output (7) blown into the storage area is sufficiently high with respect to a set temperature becomes identical to that described above with reference to FIG. 1. As the temperature within the storage area is lowered and the temperature of the air output (7) blown into the storage area approaches the set temperature, the temperature controller (10) issues an instruction that an opening angle of a valve (5) should be increased. As a result, a part of the refrigerant gas at a high temperature and at a high pressure leaving the compressor (1) would enter the evaporator (4) without discharging heat, so that the quantity of heat taken away from the ambient air by the refrigerant is reduced. In other words, the refrigerating capability is lowered.
As the temperature of the air output (7) further approaches the set temperature, the temperature controller (10) issues an instruction that the opening angle of the valve (5) should be further increased. As a result, the temperature of the air output (7) can coincide with the set temperature under a stable condition, and at this moment, the refrigerating capability coincides with the refrigerating load. At this time, the temperature of the return air (6) becomes higher than that of the air output (7) by a value equal to the refrigerating load divided by a heat capacity of the circulating air. In this way, it becomes possible to place a set temperature very close to a freezing point of the goods in the case of the cooling operation by controlling the temperature of the air output (7) that is at a lower temperature.
However, in the case of the heating operation, the situation becomes different from the above-described one. At this time, the operation of the refrigerating cycle is not always necessary, and the following description will be made with respect to the case where the circulating air is heated by a heater (11). When a current is passed through the heater (11) in response to an instruction from the temperature controller (10), the return air (6) to the refrigerating apparatus is heated by the heater (11) and converted into an air output (7) at a higher temperature which is blown out into the storage area.
If the temperature of the air output (7) detected by the temperature detector (9) reaches a predetermined temperature, then the temperature controller 10 stops feeding a current to the heater (11) and the heating operation is thereby interrupted. When the temperature within the storage area has lowered due to outflow of heat to the exterior and the temperature of the air output (7) has become lower than the set temperature by at least a predetermined value, the temperature controller (10) again instructs the passing of a current through the heater (11) to recommence the heating operation.
In the above-mentioned case, since the temperature of the return air (6) becomes lower than the temperature of the air output (7), when the set temperature is placed close to the freezing point of the goods, the temperature of the return air (6) would become lower than the freezing point, resulting in the freezing of the goods. Consequently, in the case of the system shown in FIG. 2, there is also a shortcoming in that the set temperature cannot be preset in the proximity of the freezing point of the goods.